Peridotitic diamonds from the Slave and the Kaapvaal cratons—similarities and differences based on a preliminary data set

A comparison of the diamond productions from Panda (Ekati Mine) and Snap Lake with those from southern Africa shows significant differences: diamonds from the Slave typically are un-resorbed octahedrals or macles, often with opaque coats, and yellow colours are very rare. Diamonds from the Kaapvaal are dominated by resorbed, dodecahedral shapes, coats are absent and yellow colours are common. The first two features suggest exposure to oxidizing fluids/melts during mantle storage and/or transport to the Earth's surface, for the Kaapvaal diamond population.

Comparing peridotitic inclusions in diamonds from the central and southern Slave (Panda, DO27 and Snap Lake kimberlites) and the Kaapvaal indicates that the diamondiferous mantle lithosphere beneath the Slave is chemically less depleted. Most notable are the almost complete absence of garnet inclusions derived from low-Ca harzburgites and a generally lower Mg-number of Slave inclusions.

Geothermobarometric calculations suggest that Slave diamonds originally formed at very similar thermal conditions as observed beneath the Kaapvaal (geothermal gradients corresponding to 40–42 mW/m² surface heat flow), but the diamond source regions subsequently cooled by about 100–150 °C to fall on a 37–38 mW/m² (surface heat flow) conductive geotherm, as is evidenced from touching (re-equilibrated) inclusions in diamonds, and from xenocrysts and xenoliths. In the Kaapvaal, a similar thermal evolution has previously been recognized for diamonds from the De Beers Pool kimberlites. In part very low aggregation levels of nitrogen impurities in Slave diamonds imply that cooling occurred soon after diamond formation. This may relate elevated temperatures during diamond formation to short-lived magmatic perturbations.

Generally high Cr-contents of pyrope garnets (inside and outside of diamonds) indicate that the mantle lithosphere beneath the Slave originally formed as a residue of melt extraction at relatively low pressures (within the stability field of spinelperidotites), possibly during the extraction of oceanic crust. After emplacement of this depleted, oceanic mantle lithosphere into the Slave lithosphere during a subduction event, secondary metasomatic enrichment occurred leading to strong re-enrichment of the deeper (>140 km) lithosphere. Because of the extent of this event and the occurrence of lower mantle diamonds, this may be related to an upwelling plume, but it may equally just reflect a long term evolution with lower mantle diamonds being transported upwards in the course of “normal” mantle convection.     

Temporal change of C-isotope signatures and methanogenic pathways in rice field soil incubated anoxically at different temperatures

Production of CH₄ and CO₂ was quantified in anoxically incubated soil samples taken from an Italian rice field. The rates increased with temperature between 10 and 37°C. The δ¹³C of the accumulated CO₂, CH₄ and acetate changed with time in a systematic way. The data were used in mass balance equations to constrain isotopic fractionation factors and pathways of CH₄ production. The calculations were further constrained by the determination of ¹⁴CH₄ production from ¹⁴CO₂ at steady state. At 50°C, CH₄ was exclusively produced from CO₂, indicating a fractionation factor of α_CO2/CH4 = 1.073. Between 10 and 37°C, the results showed a temporal change in the methanogenic pathway. A relatively high (40-60%) CO₂-derived fraction of CH₄ production in the beginning was followed by a phase in which contribution of CO₂-derived CH₄ decreased to low (<15%) values, and ultimately by the steady state phase in which values increased to <40% (the theoretically expected value). The rate of change from one phase to the next increased with temperature. Incubation temperature had a strong effect on the overall fractionation of ¹³C during the formation and consumption of acetate, with stronger fractionation at low than at high temperature. The results further showed that, especially at low temperatures, fractionation occurred during acetate turnover and acetoclastic methanogenesis, despite the fact that steady-state conditions caused (apparent) substrate-limitation.     

Association of calcium with colloidal particles and speciation of calcium in the Kalix and Amazon rivers

A considerable amount of colloidally bound Ca has been detected in water samples from Amazonian rivers and the Kalix River, a sub-arctic boreal river. Fractionation experiments using several analytical techniques and processing tools were conducted in order to elucidate the matter. Results show that on average 84% of the total Ca concentration is present as free Ca. Particulate, colloidal and complexed Ca constitute the remaining 16%, of which the colloidal fraction is significant. Ultrafiltration experiments show that the colloidal fraction in the sampled Amazonian rivers and the Kalix River range between 1% and 25%.In both the Amazonian and the Kalix rivers the technique of cross-flow ultrafiltration was used to isolate particles and colloids. The difference in concentration measured with ICP-AES and a Ca ion-selective electrode in identical samples was used to define the free Ca concentration and thus indirectly the magnitude of the particulate, colloidal and complexed fractions. Results from the Kalix and Amazonian rivers are in excellent agreement. Furthermore, the results show that the colloidal concentrations of Ca can be greatly overestimated (up to 227%) when conventional analysis and calculation of ultrafiltration data is used due to retention of free Ca ions during the ultrafiltration process. Calculation methods for colloidal matter are presented in this work, using complementary data from ISE analysis.In the Kalix River temporal changes in the fractionation of Ca were studied before, during and after a spring-flood event. Changes in the size distribution of colloidally associated Ca was studied using FlFFF (Flow Field-Flow Fractionation) coupled on-line to a HR ICP-MS. The FlFFF-HR ICP-MS fractograms clearly show the colloidal component of Ca, supporting the ultrafiltration findings. During winter conditions the size distribution of colloidally associated Ca has a concentration maximum at ∼5 to 10 nm in diameter, shifting to smaller sizes (<5 nm) during and after the spring flood. This shift in size distribution follows a change in the river during this period from ironoxyhydroxy colloids being the most important colloidal carrier phase to humic substances during and after the spring flood.WHAM and NICA-Donnan models were used to calculate the amount of colloidally bound Ca. The results similar for both models, show that on average 16% of the Ca may be associated to a colloidal phase, which is in broad agreement with the measurements.     

Investigation of the pyrolytic liberation of molecular nitrogen from Palaeozoic sedimentary rocks

Open-system non-isothermal pyrolysis up to 1,200°C in combination with elemental analysis was used to study the thermal liberation of molecular nitrogen (N₂) from sedimentary rocks and kerogen concentrates of Palaeozoic age from the Central European Basin system and an Eocene shale (Liaohe Basin, China) with a high content (36%) of ammonium feldspar (buddingtonite). The N/C_org (atomic) ratios of the kerogen concentrates ranged from 0.005 to 0.014, which represents the range commonly observed for coals. Bulk N/C_org ratios of the Palaeozoic shales extended from 0.035 to 0.108, indicating the presence of significant amounts of inorganic nitrogen. Namurian A and A-B (CnA; CnA-B) samples typically exhibited the earliest onset of N₂ generation with intense, characteristic peaks around 600°C. N₂ liberation from the buddingtonite-rich sample occurred at higher temperatures, with a broad peak around 700°C. Pyrograms of the kerogen concentrates showed no or strongly reduced N₂ generation in the 500–700°C range. On-line isotope-specific analysis of the pyrolytically liberated N₂ on one sample revealed a variability of ∼10‰ in the δ¹⁵N values and a steady increase in δ¹⁵N with temperature during the main phase of N₂ generation.     

On the Toxicity and Biodegradation of Cationic Surfactants Über die Toxizität und den biologischen Abbau kationischer Tenside

Three ammonium halide type surfactants were tested under standard laboratory condition for biodegradability and acute toxicity to Daphnia magna and in the Microtox test with the luminescent bacterium Photobacterium phosphoreum. The tested compounds are dimethyldistearylammonium chloride (DSDMAC), cetyltrimethylammonium bromide (HTMAB) and cetylbenzyldimethylammonium chloride (HBDMAC). The results indicate DSDMAC is less toxic than the other two surfactants and that it biodegrades rapidly at both lower (2.5 mg/L) and higher (10 mg/L) concentrations.     

Collision of the Kronotskiy arc at the NE Eurasia margin and structural evolution of the Kamchatka–Aleutian junction

Structural evolution of the Kamchatka–Aleutian junction area in late Mesozoic and Tertiary was generally controlled by (1) the processes of subduction in Kronotskiy and Proto-Kamchatka subduction zones and (2) collision of the Kronotskiy arc against NE Eurasia margin. Two structural zones of the pre-Pliocene age and six structural assemblages are recognized in studied region. 1: Eastern ranges zone comprises SE-vergent thrust folded belt, which evolved in accretionary and collisional setting. Two structural assemblages (ER1 and ER2), developed there, document shortening in the NW–SE direction and in the N–S direction, respectively. 2: Eastern Peninsulas zone generally corresponds to Kronotskiy arc terrane. Four structural assemblages are recognized in this zone. They characterize (1) precollisional deformations in the accretionary wedge (EP1) and in the fore-arc basin and volcanic belt (EP2), and (2) syn-collisional deformation of the entire Kronotskiy terrane in plunging folds (EP3) and deformations in the foreland basin (EP4). Analysis of paleomagnetic declinations versus present day structural strike in the Kronotskiy arc terrane shows that originally the arc was trending from west to east. Relative position of the accretionary wedge, fore-arc basin and volcanic belt, as well as northward dipping thrusts in accretionary wedge indicate, that a northward dipping subduction zone was located south of the arc. The accretionary wedge developed from the Late Cretaceous through the Eocene, and it implies that the subduction zone maintained its direction and position during this time. It implies that Kronotskiy arc was neither a part of the Pacific nor Kula plates and was located on an individual smaller plate, which included the arc and Vetlovka back-arc basin. Motion of the Kronotskiy arc towards Eurasia was connected only with NW-directed subduction at Kamchatka margin since Middle Eocene (42–44 Ma). Emplacement of the Kronotskiy arc at the Kamchatka margin occurred between Late Eocene and Early Miocene. This is based on the age of syn-collisional plunging folds in Kronotskiy terrane, and provenance data for the Upper Eocene to Middle Miocene Tyushevka basin, which indicate in situ evolution of the basin with respect to Kamchatka. Collision was controlled by the common motion of the Kronotskiy arc with Pacific plate towards the northwest, and by the motion of the Eurasian margin towards the south. The latter motion was responsible for the southward deflection of the western part of the Kronotskiy arc (EP3 structures), and for oblique transpressional structures in the collisional belt (ER2 structures).     

Analysis of undisturbed layers of a waste deposit landfill – Insights into the transformation and transport of organic contaminants

Comprehensive GC/MS analysis was applied to both the mobile liquid phase (seepage water) and the immobile solid matter of discrete layers derived from a waste deposit landfill. The vertical distribution of organic compounds supports information on the transport, transfer and transformation processes with depth and, consequently, with time.Numerous low molecular weight organic contaminants of natural and xenobiotic origin were identified and partially quantified. Several were selected to act as molecular indicators for different processes. Interpretation of their occurrence and concentration profiles (considering possible waste sources) and their molecular properties allowed us to (i) differentiate immobile and mobile fractions, (ii) reveal restrictions in the vertical transport by transfer processes between particulate and water phase, (iii) identify dynamic accumulations of individual contaminants and (iv) estimate approximate residence times. In addition, intensive degradation processes were pointed out for the natural fraction of the organic matter by way of determination of specific transformation products. Besides the transformation of natural components, transformation of numerous xenobiotics was recognised. In particular, with respect to an important group of contaminants, the phthalate-based plasticisers, a detailed view of (i) the influence of transfer and transport phenomena on transformation processes as well as (ii) the consecutive appearance of different degradation steps in both seepage water and solid waste was pointed out. The information provides a valuable base for the prediction of the long term behaviour of organic contaminants in waste deposit landfills.